1. Field of the Invention
The present invention pertains to a defibrillation device, and more particularly, refers to a low profile defibrillation catheter where the current conductors are utilized as electrodes.
2. Description of the Prior Art
The implantable defibrillator requires the use of electrodes to conduct large currents through the human heart. These have typically been two or more patches stitched to the heart. These are referred to as epicardial-patch electrodes, and require the surgeon to open the chest cavity for placement.
To avoid the surgery required for the epicardial patches, electrode coils are sometimes passed into the heart chambers. These coils are known as transvenous or catheter electrodes. One coil sits just above the right heart in the right atrium (RA) location, and the other lies in the right ventricular apex (RVA).
Unfortunately, the catheter electrodes are often unable to direct sufficient current through enough of the heart muscle. For this reason, a small patch is often inserted just under the skin, on the patient's lower left side. This requires additional, but minimal, surgery. This "subcutaneous patch" is not in direct contact with the heart, but allows a current vector starting at a transvenous electrode and going through heart muscle. Thus, the subcutaneous patch assists in directing current through the heart muscle, and hence, in defibrillating the heart.
There are two primary electrical requirements for defibrillation electrodes. The first is that the resistance be low enough to allow the passage of the large current through the heart. The second requirement is that the current lines pass through the vast majority of the heart muscle. This requirement is usually met by having sufficient extent to the electrodes and by careful positioning. Thus, the primary opportunity for optimization is in lowering the electrode resistance.
FIG. 1 illustrates a schematic drawing of a patient 10 fitted with a defibrillating system of the prior art consisting of a pulse generator 12 implanted in the abdominal cavity and connected to epicardial-patch electrodes 14 and 16 by electrical-lead harness 18.